1. Field of the Invention
The invention relates to a method or associated apparatus for performing defect analysis in a semiconductor wafer processing system. More particularly, the invention relates to a method and apparatus that uses image analysis to analyze semiconductor wafers to determine defect causes and locations.
2. Description of the Background Art
Many techniques are used involving, e.g., optical systems, electron microscopes, spatial signature analysis, and energy dispersive x-ray microanalysis, to identify and analyze defects on a semiconductor wafer. To identify defects using the above defect analysis techniques, wafers are intermittently selected from a lot of wafers that is being processed, i.e., one in every N wafers is selected. The selected wafers are analyzed using one or more of the above-identified analysis techniques (these techniques are performed by tools that are commonly referred to as metrology tools). These techniques produce images and data representing a surface of the selected wafers. A skilled operator reviews the images and data recorded by the metrology tools to identify defects on the selected wafers. The source of the defect is generally identified through trial and error, i.e., changes are made in the process parameters in an attempt to eliminate the defect in a wafer selected from another lot. Some types of defects occur for well-known reasons. These defects are cataloged in a searchable database of defect data and images. An operator can compare the test results to the defect database in an attempt to match the test results to defects contained in the defect database. If a match is found, the database may identify the source of that particular type of defect. The operator can then take corrective action to eliminate the defect.
A relatively large amount of information relating to wafer defects is necessary to provide an illustrative sample of the varied and multiple defects that may occur to any semiconductor wafer that is being processed through a series of processes. Generally, a defect analysis system using a large amount of stored data can provide more effective defect comparisons than a defect analysis system using a small amount of stored data. Even large volume semiconductor processes will require a certain amount of time until sufficient numbers of wafers have been processed and analyzed to provide reliable defect source information. Unfortunately, processing semiconductor wafers is very expensive, and many companies or groups can only afford to process a relatively small number of semiconductor wafers through any prescribed set of processes for testing purposes.
Therefore, a need exists in the art for a system that can effectively analyze wafer defects and repeatedly utilize the defect source information through the use of a shared database of defect data that is accessible over a wide area network.